XML parser performance in Python 3.3

For a recent bug ticket about MiniDOM, I collected some performance numbers that compare it to ElementTree, cElementTree and lxml.etree under a recent CPython 3.3 developer build, all properly compiled and optimised for Linux 64bit, using os.fork() and the resource module to get a clean measure of the memory usage for the in-memory tree. Here are the numbers:

Parsing hamlet.xml in English, 274KB:

Memory usage: 7284
xml.etree.ElementTree.parse done in 0.104 seconds
Memory usage: 14240 (+6956)
xml.etree.cElementTree.parse done in 0.022 seconds
Memory usage: 9736 (+2452)
lxml.etree.parse done in 0.014 seconds
Memory usage: 11028 (+3744)
minidom tree read in 0.152 seconds
Memory usage: 30360 (+23076)

Parsing the old testament in English (ot.xml, 3.4MB) into memory:

Memory usage: 20444
xml.etree.ElementTree.parse done in 0.385 seconds
Memory usage: 46088 (+25644)
xml.etree.cElementTree.parse done in 0.056 seconds
Memory usage: 32628 (+12184)
lxml.etree.parse done in 0.041 seconds
Memory usage: 37500 (+17056)
minidom tree read in 0.672 seconds
Memory usage: 110428 (+89984)

A 25MB XML file with Slavic Unicode text content:

Memory usage: 57368
xml.etree.ElementTree.parse done in 3.274 seconds
Memory usage: 223720 (+166352)
xml.etree.cElementTree.parse done in 0.459 seconds
Memory usage: 154012 (+96644)
lxml.etree.parse done in 0.454 seconds
Memory usage: 135720 (+78352)
minidom tree read in 6.193 seconds
Memory usage: 604860 (+547492)

And a contrived 4.5MB XML file with a lot more structure than data and no whitespace at all:

Memory usage: 11600
xml.etree.ElementTree.parse done in 3.374 seconds
Memory usage: 203420 (+191820)
xml.etree.cElementTree.parse done in 0.192 seconds
Memory usage: 36444 (+24844)
lxml.etree.parse done in 0.131 seconds
Memory usage: 62648 (+51048)
minidom tree read in 5.935 seconds
Memory usage: 527684 (+516084)

I also took the last file and pretty printed it, thus adding lots of indentation whitespace that increased the file size to 6.2MB. Here are the numbers for that:

Memory usage: 13308
xml.etree.ElementTree.parse done in 4.178 seconds
Memory usage: 222088 (+208780)
xml.etree.cElementTree.parse done in 0.478 seconds
Memory usage: 103056 (+89748)
lxml.etree.parse done in 0.199 seconds
Memory usage: 101860 (+88552)
minidom tree read in 8.705 seconds
Memory usage: 810964 (+797656)

Yes, 2MB of whitespace account for almost 300MB more memory in MiniDOM.

Here are the graphs:

XML tree memory usage in Python 3.3 for lxml, ElementTree, cElementTree and MiniDOM

XML perser performance in Python 3.3 for lxml, ElementTree, cElementTree and MiniDOM

I think it is pretty clear that minidom has basically left the scale, whereas cElementTree and lxml.etree are pretty close to each other. lxml tends to be a tad faster, and cElementTree tends to use a little less memory.

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